The present invention relates to an illumination light transmitting device to be installed in an on-vehicle electrical equipment such as a heater control unit and adapted to illuminate a radio, for example, to be arranged under the heater control unit, and more particularly to an illumination light transmitting device suitable for the case where an illumination light source is obliged to be located at an extreme end of an illumination range.
FIG. 2 shows a conventional illumination light transmitting device. Reference numeral 2 designates an illumination light transmitting body having an illuminating portion 2a formed with plural sawtoothed grooves 2e. The illumination light transmitting body 2 is provided in a case 1 forming a part of a front panel A of a heater control unit. The case 1 defines a substantially L-shaped space therein having at one end thereof a holder portion 1a for receiving a light source 3.
The illumination light transmitting body 2 is formed of a material having a good light transmittance such as glass and acrylic resin, and it is formed in a rectangular shape. The illumination light transmitting body 2 has a light receiving portion 2b at one end portion thereof disposed near and opposite to the light source 3 received in the holder portion 1a of the case 1. The light receiving portion 2b is formed with a light reflecting surface 2c for reflecting the light from the light source 3 and transmitting the reflected light into the illumination light transmitting body 2. The illuminating portion 2a is formed at the other end portion of the illumination light transmitting body 2, and it is formed with an oblique surface 2d substantially parallel to the light reflecting surface 2c. The oblique surface 2d of the illuminating portion 2a is formed with the sawtoothed grooves 2e for reflecting the light transmitted through the illumination light transmitting body 2 toward an opening portion 5 of the front panel A through a color board 4 covering the opening portion 5 to an objective body 6 to be illuminated.
However, in the conventional illuminating construction wherein the light transmitted through the illumination light transmitting body 2 is reflected by the sawtoothed grooves 2e to illuminate the objective body 6, the light reflected by the light reflecting surface 2c is repeatedly reflected with irregular reflection on an upper surface 2f and a lower surface 2g of the illumination light transmitting body 2 until it reaches the oblique surface 2d of the illuminating portion 2a. Therefore, the light enters the sawtoothed grooves 2e at complex incident angles. Thus, as the light with the complex incident angles is reflected by the flat surfaces of the sawtoothed grooves 2e, the effect of the irregular reflection causes a lack of uniform illumination and less light quantity at a position far away from the light source 3.